Brain Illustration 

Can marijuana affect teen brain development?

WHAT WE KNOW:  Some negative effects of marijuana on teen brain development have been shown. The prefrontal cortex does not reach full maturity until the early twenties, meaning that many complex processes of the adolescent brain are still in progress. Neuroscientific research indicates that during this time, teens are especially vulnerable to the effects of cannabis. Delaying or preventing the start of regular marijuana use to adulthood can prevent long-term damage to neurons and ensure optimal brain health and functioning.

WHAT WE'RE WATCHING:  We need more research regarding the impact of cannabis on brain development and neurocognition. We also need resources to help prevent and delay the start of cannabis use.

Brain Impulses Image

How does marijuana affect teens’ control of impulses and emotions?

WHAT WE KNOW:  Teen marijuana smokers often have less self-control, which can lead to unsafe behavior. Brain imaging shows that regular users of marijuana have less gray matter than nonusers in the region of the brain that contributes to impulse control, as well as to decision making and learning. Additionally, results of multiple studies have found that teens who started using marijuana at a young age showed less control of inhibitions. Because the prefrontal cortex and other areas of the brain are vulnerable in youth, cannabis can reduce impulse control and emotional regulation.

WHAT WE'RE WATCHING:  Amount, potency and length of use make a difference, but we don’t know how much. The next step for this research is to continue to study and compare the effects of marijuana use on teen brains over time.

Does cannabis use reduce teen IQ?

WHAT WE KNOW:  The simple answer is yes. Heavy marijuana use starting in teens or younger may lower IQ by as many as eight points. And the loss of IQ is permanent. Heavy use also causes loss in brain processing speed and memory.*

WHAT WE'RE WATCHING:  More testing can help find out how other factors, possibly including family, environment, how much use, and how often, may play a part.

*This study followed over 1,000 cannabis users from ages 13 to 38 years of age.

“Adolescence is the absolute worst time to introduce mind-altering drugs, such as marijuana, because it can disrupt development. Think of the teen years as the last golden opportunity to make the brain as healthy and smart as possible."

Krista Lisdah, PhD, Director, Brain Imaging and Neuropsychology Lab, University of Wisconsin, Milwaukee